ITUpSat-1 is a student designed and developed picosatellite of ITU (Istanbul Technical University), Istanbul, Turkey. The picosatellite conforms to the CubeSat standards with side lengths of 10 cm and a mass of ≤ 1 kg. 1)2)3)

The overall objectives are to provide a hands-on project environment for the students at ITU under faculty guidance. The mission goals are to capture imagery of the CMOS payload and to study the behavior of the passive stabilization system of the CubeSat. 4)

The spacecraft structure was purchased from Pumpkin Inc. of San Francisco, CA, consisting of aluminum 6061&5052 material (CubeSat Kit by Pumpkin Inc.). The are 3 identical side faces and one face with access ports. The spacecraft stabilization concept is discussed under Payload 1. 5)

EPS (Electrical Power Subsystem): The EPS consists of face-mounted solar panels, a regulator board and associated batteries (Li-polymer). The system is able to charge itself (maximum power point tracking) and provide a regulated 3.3 V and 5 V bus service. The EPS was provided by Clyde Space.

Design of a deployable antenna system for a CubeSat: The base concept is shown in Figure 4 after investigating a number of various alternatives (Ref. 1). The pin mechanism selected includes bases to attach the antennas and pins to wrap them around. The pins and bases are attached to the solar panels with small screws. The cables are routed to a connector outside for connection to the antennas. 6)

Figure 4: Final configuration of the deployable antenna system featuring a pin mechanism (image credit: ITU)

OBC (On-board Computer): The FM430 flight module of Pumpkin Inc. is being used. The FM430 is a compact solution for harsh environment systems. It has an SD (Secure Digital) card interface, one USB (Universal Serial Bus) port and external power supply connector. Also an interface to MHX series radio modems from Microhard Systems is available on the flight module. The FM430 is equipped with an MSP430F1611 microcontroller, a 16 bit 8 MHz low power microcontroller from Texas Instruments. It has many peripherals such as I2C (Inter-Integrated Communication), SPI (Serial Peripheral Interface), UART (Universal Asynchronous Receiver/Transmitter) buses, and also supports DMA (Direct Memory Access). It has a flash memory of 55 kB and 10 kB of RAM. The microcontroller unit consumes 100 mW of power at most.

RF communications: The primary on-board communication system is the MHX-425 transceiver from Microhard Systems. This frequency hopping spread spectrum radio which works in the UHF band has adjustable hopping patterns, a high sensitivity (-115 dBm), and output power of up to 1 W (437.325 MHz, GFSK modulation), the date rate is 19.2 kbit/s. The transceiver interfaces directly to the on-board computer, it has a mass of about 80 gram.

In addition, ITUpSat-1 features a beacon for easy identification and continuous reporting of critical telemetry. Unlike the other transceiver, it will always be on during the orbit and will be transmitting identification and simple telemetry in CW (e.g. Morse code) every two minutes. This means anyone with the knowledge of the orbital parameters (in particular the amateur radio community) can easily pick up our signal. The beacon has a 100 mW RF output capacity.

Figure 6: Schematic view of onboard elements (image credit: ITU)

Figure 7: Photo of the inner structure of ITUpSat (image credit: ITU)

Figure 8: Photo of ITUpSat-1 prior to launch (image credit: ITU)

Launch: ITUpSat-1 was launched on Sept. 23, 2009 as a secondary payload on a PSLV launcher (PSLV-C14) of ISRO (launch provider: Antrix Corporation). The SPL (Single Picosatellite Launcher) system of Astrofein (Astro und Feinwerktechnik Adlershof GmbH, Berlin, Germany) is being used to deploy the 4 CubeSats. The launch service interface for all CubeSats is provided by ISIS (Innovative Solutions In Space BV) of Delft, The Netherlands.

The launch site was the SDSC‐SHAR (Satish Dhawan Space Center-Sriharikota) on the east coast of India. The primary payload on the flight is OceanSat-2 of ISRO (Indian Space Research Organization) with a launch mass of 960 kg.

• On Sept. 23, 2013, the ITUpSat-1 CubeSat was 4 years on orbit, operating nominally.

• The ITUpSat-1 spacecraft is operating nominally in 2012 (in the third year of operations, Ref. 9).

• The ITUpSat-1 spacecraft is operating nominally in the spring of 2011. - Aside from the ITU ground station, the ITUpSat-1 beacon signal has been received and identified by many countries (including Japan, Norway, Italy, Germany and USA) as well as by amateur radio operators around Turkey. 7)8)

• In late October 2010, the spacecraft is sending continuously its beacon signals, permitting the project to operate the spacecraft. Analysis of the data shows that the batteries, the solar cells and panels, the OBC, the passive stabilization system, etc., are all working nominally. 9)

• On Sept. 23, 2010, the ITUpSat-1 CubeSat was one year in orbit.

• The on-board modem failed shortly after the launch. Hence, only beacon signals are available providing the housekeeping data of the spacecraft. In the aftermath, the project asked the amateur radio community to track the CubeSat for additional telemetry data of the spacecraft.

Sensor complement: (Payload 1, Payload 2)

The CubeSat features two payloads. The first one is a sensor suite with an IMU and a magnetometer, and the second one is a low-resolution CMOS imager. The two payloads share a microcontroller and are physically on the same PCB representing the uppermost circuit of the electronics stack of the satellite.

Payload 1:

This subsystem represents the attitude sensing and passive stability hardware. It consists of three gyros, a three-axis accelerometer both from Analog Devices in addition to a three-axis magnetometer (Honeywell), and an AlNiCo magnet. The magnetometer will help to counter the inherent bias and drifts of inertial sensors and provide measurement updates for a filtered and corrected solution of the attitude. The analog-digital conversion of all the sensor outputs is done by a PIC microprocessor which also has the task of grouping the measurements into a packet and sending them over the I2C bus to the OBC for downlink transmission.

Payload 2:

Payload 2 is a low-resolution CMOS camera with a detector array of 640 x 480 pixels (COTS imager based on the OV7620 image sensor). The objective is to take snapshot imagery. An interface board is designed to integrate camera with the MSP430F1611 microcontroller.

The camera can be operated in VGA/QVGA (Video Graphics Array/Quarter Video Graphics Array) modes, transfer images in 8/16 bit modes and can be controlled over the I2C bus.

Ground segment:

A ground station was built at ITU for the operations (monitoring and control services) of ITUpSat-1. The MHX modem (Microhard Systems) is also installed in the ground station for communication with the satellite's nominal communication system.

The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net)